1. Field of the Invention
The present invention relates to a display device such as a liquid crystal display device which is used, for example, for office automation equipment (e.g., a word processor, a personal computer, or the like) or a television set.
2. Description of the Related Art
FIG. 19 shows a configuration of an active matrix substrate which is a part of a conventional liquid crystal display device.
This liquid crystal display device is of the active matrix type in which the active matrix substrate and a counter substrate are disposed so as to face each other with a display medium made of liquid crystals or the like interposed therebetween. The active matrix substrate includes thin-film transistors (hereinafter, referred to as xe2x80x9cTFTsxe2x80x9d) 2 serving as switching elements and pixel capacitances 1 disposed in a matrix.
Gate signal lines 3 each serving as a scanning line for controlling the TFTs 2 are connected to a gate electrode of the respective TFTs 2, thereby driving the TFTs 2 by a signal input thereto. Source signal lines 5 each serving as a signal line for supplying a data signal to the TFTs 2 are connected to a source electrode of the respective TFTs 2, allowing a video signal or the like to be input therefrom. The gate signal lines 3 and the source signal lines 5 are provided so as to cross each other in the vicinity of the TFTs 2.
A pixel electrode 6 and one terminal (i.e., an electrode) of the pixel capacitance 1 are connected to a drain electrode of the TFT 2. The other terminal (i.e., an electrode) of the pixel capacitance 1 is connected to a pixel capacitance line 4. The pixel capacitance lines 4 are electrically connected to a counter electrode formed on the counter substrate in the completed configuration of the liquid crystal display device.
FIG. 20 is a cross-sectional view illustrating the conventional active matrix substrate.
The active matrix substrate includes a gate electrode 12, which is a part of the gate signal line 3, provided on a transparent insulating substrate 11, and a gate insulating film 13 provided so as to cover the gate electrode 12. On the gate insulating film 13, a semiconductor layer 14 is provided so as to overlap the gate electrode 12. A channel protecting layer 15 is provided above a center portion of the semiconductor layer 14. Furthermore, n+-Si layers 16a and 16b to be a source electrode and a drain electrode, respectively, are provided so as to cover edge portions of the channel protecting layer 15 and parts of the semiconductor layer 14 and so as to be separated from each other on the channel protecting layer 15.
An ITO (Indium Tin Oxide) film 9a and a metal layer 17a to be a source signal line 5 are sequentially provided on a part of the n+-Si layer 16a. An ITO film 9b and a metal layer 17b to be a connecting electrode for connecting a drain electrode and a pixel electrode 20 (not shown) are sequentially provided on a part of the n+-Si layer 16b. 
A passivation film 18 made of an inorganic thin film is provided on the resultant substrate, and an interlayer insulating film 19, formed of an organic thin film having a high transparency, is provided thereon so as to cover the TFT 2, the gate signal line 3, and the source signal line 5. The pixel electrode 6 is formed on the interlayer insulating film 19. The pixel electrode 6 is connected to the n+-Si layer 16b, i.e., the drain electrode of the TFT 2, by the ITO film 9b which functions as the connecting electrode via a contact hole 7 penetrating through the passivation film 18 and the interlayer insulating film 19.
However, in the case where the gate insulating film 13 and the passivation film 18 made of the inorganic thin film are present between the transparent insulating substrate 11 and the interlayer insulating film 19 made of the organic thin film having a high transparency as in the above, light reflection occurs due to differences in refractive indexes at the interface of the substrate 11 and the gate insulating film 13 and at the interface of the passivation film 18 and the interlayer insulating film 19.
As a result of such reflection, there arises a problem of reduced light transmittance.
A display device of the present invention has a pair of substrates provided so as to face each other with a display medium interposed therebetween, and further includes, on a first substrate of the pair of substrates: switching elements disposed in a matrix; scanning lines and signal lines disposed so as to cross each other; and an interlayer insulating film provided so as to have the switching elements, the scanning lines and the signal lines on one surface thereof and pixel electrodes on the other surface thereof. Each of the pixel electrodes is electrically connected to a drain electrode of one of the switching elements via a contact hole which penetrates through the interlayer insulating film. The interlayer insulating film is made of an organic thin film having a high transparency and covers at least the switching elements, the scanning lines and the signal lines. Furthermore, the interlayer insulating film is provided so as to contact directly with the first substrate in a light-transmitting area which is not shaded at least by the switching elements, the scanning lines and the signal lines.
In one embodiment, the display device further includes: a gate insulating film at least covering a gate electrode of each of the switching elements; and a passivation film, made of an inorganic thin film, at least covering the switching elements. The gate insulating film and the passivation film are provided between the first substrate and the interlayer insulating film in a region excluding the light-transmitting area. The gate insulating film is a first patterned film which is provided to cover both the light-transmitting area and the region excluding the light-transmitting area on the first substrate and then partially removed in the light-transmitting area. The passivation film is a second patterned film which is provided to cover both the light-transmitting area and the region excluding the light-transmitting area on the first substrate and then partially removed in the light-transmitting area.
In another embodiment, the display device further includes a gate insulating film at least covering a gate electrode of each of the switching elements. The gate insulating film is provided between the first substrate and the interlayer insulating film in a region excluding the light-transmitting area. The gate insulating film is a patterned film which is provided to cover both the light-transmitting area and the region excluding the light-transmitting area on the first substrate and then partially removed in the light-transmitting area.
Preferably, a refractive index of the interlayer insulating film is in the range of about 1.5 to about 2.0.
In one embodiment, the display device further includes a gate insulating film provided on the gate electrodes of each of the switching elements and the scanning lines and under the signal lines between the first substrate and the interlayer insulating film in a region excluding the light-transmitting area. The gate insulating film is a first patterned film which is provided to cover both the light-transmitting area and the region excluding the light-transmitting area on the first substrate and then partially removed in the light-transmitting area while retained on the gate electrodes and the scanning lines and under the signal lines.
Preferably, the display device further includes a passivation film made of an inorganic thin film. The passivation film is provided on the switching elements and the scanning lines and under the signal lines between the first substrate and the interlayer insulating film in the region excluding the light-transmitting area. The passivation film is a second patterned film which is provided to cover both the light-transmitting area and the region excluding the light-transmitting area on the first substrate and then partially retained in the light-transmitting area while retained on the switching elements, the scanning lines and the signal lines.
A first portion of the passivation film located on the scanning lines may be provided so as to cover the edges of a first portion of the gate insulating film located on the scanning lines, and a second portion of the passivation film located on the signal lines may be provided so as to cover the edges of a second portion of the gate insulating film located under the scanning lines.
The passivation film may be patterned by dry-etching.
A pattern width of the gate insulating film may be increased at respective crossing areas of the scanning lines and the signal lines, at a bending portion of a pattern of the scanning lines, and at a bending portion of a pattern of the signal lines.
Similarly, a pattern width of the passivation film may be increased at respective crossing areas of the scanning lines and the signal lines, at a bending portion of a pattern of the scanning lines, and at a bending portion of a pattern of the signal lines.
A display device, to be provided in accordance with another aspect of the present invention, includes a pair of substrates provided so as to face each other with a display medium interposed therebetween, and further includes, on a first substrate of the pair of substrates: switching elements disposed in a matrix; scanning lines and signal lines disposed so as to cross each other; and an interlayer insulating film provided so as to have the switching elements, the scanning lines and the signal lines on one surface thereof and pixel electrodes on the other surface thereof, each of the pixel electrodes being electrically connected to a drain electrode of one of the switching elements via a contact hole which penetrates through the interlayer insulating film. The display device further includes, between the first substrate and the interlayer insulating film, at least one of a gate insulating film, which at least covers a gate electrode of each of the switching elements, and a passivation film, which is made of an inorganic thin film and at least covers the switching elements. The interlayer insulating film is made of an insulating film having a high transparency and a refractive index in the range of about 1.8 to about 2.0.
Thus, the invention described herein makes possible the advantage of providing a display device capable of realizing a bright display by improving light transmittance.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.